Every NV tube is different, this is why it’s important to get (and KEEP) your data sheet for your unit/tube. It’s like the pedigree for a high dollar dog, it proves it’s origin, how it performs, etc.
Kind of “proving it’s worth” also in a way.
That being said, without knowing actual specs on the other units, we can just guess how these would compare. Please keep in mind these are just estimations-
So let’s say the “then PVS14s before that” statement refers to a green phosphor PVS14, again unknown origin, if you have a TIME PERIOD you are talking about that would help also.
The White Phosphor alone is going to give the impression of more brightness and clarity, even if by chance you had a green tube and a white tube that had very similar specifications.
OVERALL, we see much higher specifications currently in White Phosphor tubes versus green phosphor. This coupled with the fact that hardly anyone orders green phosphor any more, led us to stop ordering green phosphor tubes. We would get in 50 tubes of green, 50 of white and the white would sell out meanwhile 45 of the 50 greens would still be sitting there. Also, the whites ended up with higher OVERALL specifications, which means more performance, which means happier customers 
We offer a couple varieties in White Phosphor tube PVS14s-
PVS14 WP3 that utilizes the MID GRADE Elbit Systems of America (formerly ITT) SLH grade of thin film tubes. Don’t let the price confuse you, these are NOT the “bottom of the barrel” xls grade of tubes. The SLH mid grade tubes are big step up from the xls tubes which can have a ton of blems, numbers all out of whack, etc. The WP3s with SLH mid grade tubes offer the best bang for the buck in WP and currently on sale stupid cheap for the holidays.
PVS14 WP3 High grade models utilize the VH and YH Elbit Systems of America tubes. These are the highest commonly available grade of thin film tubes Elbit makes. These will in general be slightly cleaner and have a little better OVERALL specification numbers than the mid grade SLH tube units above. In a batch of 50 tubes, we sell usually 48 or so of them coming in at 2200 FOM or higher, so we rarely get a lot of 1900-2200 FOM models of these.
PVS14 WP3 UF features an Un Filmed or “filmless” L3 Harris White Phosphor 20UM grade tube. Most places sell the 18um lower grade tubes, we noticed the 20UM higher grade L3 tubes were coming out much cleaner and better numbers than the 18um so we only order 20UM now. Like the Elbit “high grade” systems, we normally just see 2200 FOM and higher performing tubes in this class as well.
Now on to your compare to a 31 question.
PVS31s are DUAL TUBE sets, so different than a PVS14 which is a monocular. If you know actual specs from the data sheet on the 31s, I could give you a better idea about comparing.
For dual tube sets, we have the New Katana articulating bino sets with high grade YH White phosphor tubes in stock and shipping out quickly.